Cy A. Stein

FDA-Approved Oligonucleotide Therapies in 2017

Oligonucleotides (oligos) have been under clinical development for approximately the past 30 years, beginning with antisense oligonucleotides (ASOs) and apatmers and followed about 15 years ago by siRNAs. During that lengthy period of time, numerous clinical trials have been performed and thousands of trial participants accrued onto studies. Of all the molecules evaluated as of January 2017, the regulatory authorities assessed that six provided clear clinical benefit in rigorously controlled trials. The story of these six is given in this review.

Targeting angiopoietin-2 signaling in cancer therapy

Introdcution: Over the past decade, several anti-angiogenic strategies have been devised to target a wide spectrum of malignancies. The most widely utilized approach involves abrogation of vascular endothelial growth factor receptor signaling through either consumption of ligand (i.e., with the monoclonal antibody bevacizumab) or through direct inhibition of the receptor tyrosine kinase domain (i.e., with small molecules such as sunitinib or sorafenib). While these agents do appear to delay cancer progression in the clinic, they are not curative approaches. Areas covered: A novel anti-angiogenic strategy involves inhibition of signaling along the Ang/Tie-2 axis, a pathway critical for mediating endothelial and perivascular cell interactions. While several agents (i.e., AMG-386 and regorafenib) have reached late stages of clinical development, others (i.e., ARRY614 and CEP-11981) are in their relative infancy. Herein, we will outline the clinical trajectory of wide spectrum Ang/Tie-2 inhibitors, with attention to data evaluating combinations with cytotoxic therapy or other targeted agents. Expert opinion: Provided that these approaches to not drastically augment toxicity, they may represent the ideal path for further development of this class of agents.

Antisense 2′-Deoxy, 2′-Fluoroarabino Nucleic Acid (2′F-ANA) Oligonucleotides: In Vitro Gymnotic Silencers of Gene Expression Whose Potency Is Enhanced by Fatty Acids

Gymnosis is the process of the delivery of antisense oligodeoxynucleotides to cells, in the absence of any carriers or conjugation, that produces sequence-specific gene silencing. While gymnosis was originally demonstrated using locked nucleic acid (LNA) gapmers, 2′-deoxy-2′fluoroarabino nucleic acid (2′F-ANA) phosphorothioate gapmer oligonucleotides (oligos) when targeted to the Bcl-2 and androgen receptor (AR) mRNAs in multiple cell lines in tissue culture, are approximately as effective at silencing of Bcl-2 expression as the iso-sequential LNA congeners. In LNCaP prostate cancer cells, gymnotic silencing of the AR by a 2′F-ANA phosphorothioate gapmer oligo led to downstream silencing of cellular prostate-specific antigen (PSA) expression even in the presence of the androgenic steroid R1881 (metribolone), which stabilizes cytoplasmic levels of the AR. Furthermore, gymnotic silencing occurs in the absence of serum, and silencing by both LNA and 2′F-ANA oligos is augmented in serum-free (SF) media in some cell lines when they are treated with oleic acid and a variety of ω-6 polyunsaturated fatty acids (ω-6 PUFAs), but not by an aliphatic (palmitic) fatty acid. These results significantly expand our understanding of and ability to successfully manipulate the cellular delivery of single-stranded oligos in vitro.

A cytoplasmic pathway for gapmer antisense oligonucleotide-mediated gene silencing in mammalian cells

Antisense oligonucleotides (ASOs) are known to trigger mRNA degradation in the nucleus via an RNase H-dependent mechanism. We have now identified a putative cytoplasmic mechanism through which ASO gapmers silence their targets when transfected or delivered gymnotically (i.e. in the absence of any transfection reagent). We have shown that the ASO gapmers can interact with the Ago-2 PAZ domain and can localize into GW-182 mRNA-degradation bodies (GW-bodies). The degradation products of the targeted mRNA, however, are not generated by Ago-2-directed cleavage. The apparent identification of a cytoplasmic pathway complements the previously known nuclear activity of ASOs and concurrently suggests that nuclear localization is not an absolute requirement for gene silencing.

Antisense oligonucleotides in cancer.

Purpose of review Over the past several dozen years, regardless of the substantial effort directed toward developing rational oligonucleotide strategies to silence gene expression, antisense oligonucleotide-based cancer therapy has not been successful. This review focuses on the most likely reasons for this lack of success, and on the barriers that still need to be overcome to make a clinical cancer treatment reality out of the promise of antisense therapy. Recent findings Considerable progress has been made in the design and delivery of nucleic acid fragments. Chemical modifications have considerably improved oligonucleotide absorption, distribution and metabolism while at the same time reducing toxicity. Nevertheless, the delivery and the cellular uptake of these molecules are still not adequate to provide the desired therapeutic outcome. Recent therapeutic interventional phase III trials of antisense oligodeoxyribonucleotides for a cancer indication will be discussed, in addition to those studies that markedly improve the scientific understanding of the properties of these molecules. Summary We still do not have a marketed antisense oligonucleotide for a cancer indication. This is because critical aspects of the cellular, tumor pharmacology and delivery properties of these agents are still not well understood.

Enzalutamide for the treatment of prostate cancer.

Introduction: The FDA approval of docetaxel for metastatic castration-resistant prostate cancer (mCRPC) in 2005 marked a major milestone, as it was the first approved agent for this disease that demonstrated a survival advantage in Phase III assessment of this disease. Since 2009, several other agents have been approved by FDA, including sipuleucel-T, abiraterone, cabazitaxel and enzalutamide. Enzalutamide, a potent antiandrogen that blocks nuclear translocation of the androgen receptor (AR), is the most recently approved of these agents. Areas covered: The clinical development of enzalutamide is discussed, with attention given as to how this agent will most appropriately be used among a growing list of agents for mCRPC. A MEDLINE search was conducted to identify all relevant published datasets pertaining to the drug. In addition, relevant ASCO and ESMO abstracts were searched. Expert opinion: The current role and sequencing of enzalutamide may change drastically based on studies such as PREVAIL (a Phase III pre-chemotherapy assessment of enzalutamide) and planned studies to assess relevant combinations (i.e., enzalutamide with abiraterone). Outside of clinical efficacy, issues such as drug cost may ultimately dictate our utilization of agents such as enzalutamide for mCPRC. Although the development of biomarkers to guide therapy for mCRPC is ideal, there are inherent challenges in establishing biomarker-driven treatment.

Defibrotide (Defitelio): A New Addition to the Stockpile of Food and Drug Administration-approved Oligonucleotide Drugs

On 1 April 2016, the Food and Drug Administration approved Defitelio, known for many years as Defibrotide (DF), for marketing in the United States. The indication is severe hepatic veno-occlusive disease (sVOD) following high-dose chemotherapy and autologous bone marrow transplantation, a toxicity of therapy with a high mortality. Defibrotide is not the kind of oligonucleotide drug beloved by molecular biologists and proponents of personalized medicine. Its very complicated mechanism of action, which is still elusive, is without question nonsequence specific, and almost certainly based on the charge-charge interactions of its constituents with biological macromolecules, which are almost certainly proteins.

Paclitaxel-Based High-Dose Chemotherapy with Autologous Stem Cell Rescue for Relapsed Germ Cell Tumor: Clinical Outcome and Quality of Life in Long-Term Survivors

BACKGROUND High-dose chemotherapy (HDCT) is a viable and potentially curative approach for patients with relapsed or refractory germ cell tumors (GCTs). However, no comparative data exist to define the optimal chemotherapeutic strategy, and little is known about the quality of life (QOL) of long-term survivors. Herein we attempt to characterize the QOL in long-term survivors who received high-dose paclitaxel, etoposide, carboplatin, and ifosfamide (TECTIC). PATIENTS AND METHODS Details of the TECTIC regimen and clinical outcomes for the initial 33 patients have been reported. In the present study, we report the clinical data for 15 additional patients. Using the European Organization for the Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire-Core 30 (QLQ-C30) and the Functional Assessment of Cancer Therapy-Taxane (FACT-T) questionnaires, we surveyed all patients who survived at least 4 years after HDCT. RESULTS Forty-eight patients were enrolled and 46 patients received protocol therapy. For all 48 patients, the median progression-free survival (PFS) and overall survival (OS) were 11.8 months (range, 5.8-not reached) and 21.7 months (range, 12.7-not reached), respectively. Seventeen patients were progression free at a median of 123.2 months (51.6-170.2 months), and 6 patients remain alive after progression with a median OS of 68.8 months (47.6-147.1 months). Of the 23 surviving patients, 18 were accessible and consented to telephone interviews. Compared with historical cohorts, survivors had a higher global health scale score (87.04 vs. 75.62; P = .02) but a lower physical functioning score (68.89 vs. 92.66; P = .0001) by the QLQ-C30 scale. CONCLUSIONS HDCT with the TECTIC regimen produces durable remissions in patients with relapsed or refractory GCTs with acceptable QOL in long-term survivors.

Protein Kinase C-α is a Critical Protein for Antisense Oligonucleotide-mediated Silencing in Mammalian Cells

We have identified the existence of a productive, PKC-α-dependent endocytotic silencing pathway that leads gymnotically-delivered locked nucleic acid (LNA)-gapmer phosphorothioate antisense oligonucleotides (ASOs) into late endosomes. By blocking the maturation of early endosomes to late endosomes, silencing the expression of PKC-α results in the potent reduction of ASO silencing ability in the cell. We have also demonstrated that silencing of gene expression in the cytoplasm is vitiated when PKC-α expression is reduced. Restoring PKC-α expression via a reconstitution experiment reinstates the ability of ASOs to silence. These results advance our understanding of intracellular ASO trafficking and activity following gymnotic delivery, and further demonstrate the existence of two distinct silencing pathways in mammalian cells, one in the cytoplasmic and the other in the nuclear compartment.

Preoperative therapy for localized prostate cancer: A comprehensive overview

At the 2012 American Society of Clinical Oncology (ASCO) Annual Meeting, two studies of preoperative systemic therapy for localized prostate cancer garnered significant attention. In the first, investigators evaluated various permutations of conventional hormonal therapies prior to prostatectomy, with detailed biomarker studies focused on tissue androgens. In the second, investigators assessed the novel CYP17 lyase inhibitor abiraterone prior to prostatectomy. Both studies provide a wealth of biological information, but the question remains - will preoperative systemic therapy ultimately be incorporated into clinical algorithms for prostate cancer? Herein, the existing literature for both preoperative hormonal and chemotherapeutic approaches is reviewed. We performed a MEDLINE search of published prospective and retrospective clinical studies assessing preoperative systemic therapy for prostate cancer from 1982 onwards, revealing a total of 75 publications meeting these criteria. Of these, 55 possessed a number of patients (i.e., greater than 10) deemed worth of the current analysis. Beyond outlining these datasets, we discuss the relevance of clinical and pathologic endpoints in assessing preoperative therapy.